Partial oxidation reformer-reforming exchanger arrangement for hydrogen production

ABSTRACT

A method for retrofitting a syngas process entails converting a first hydrocarbon stream to a first reactor effluent through partial oxidation; cooling the first reactor effluent and producing steam with recovered heat; and receiving the cooled reactor effluent and producing a product syngas of enhanced hydrogen content. The downstream processing entails cooling the first reactor effluent to a temperature from about 650 to about 1000 degrees C. The first reactor effluent is diverted to a reforming exchanger. A second hydrocarbon portion with steam is passed through a catalyst zone in the reforming exchanger forming a second reactor effluent. The second reactor effluent is discharged from the catalyst zone forming an admixture with the first reactor effluent. The admixture is passed across the catalyst zone in indirect heat exchange therewith to cool the admixture and heat the catalyst zone. The cooled admixture is supplied back to the reforming exchanger.

CROSS REFERENCE TO RELATED APPLICATIONS

The current application is a divisional of co-pending U.S. application Ser. No. 10/708,606, filed on Mar. 15, 2004, which claims priority to U.S. Provisional Application No. 60/320,011, filed on Mar. 16, 2003.

FIELD

The embodiments relate to methods of production of a synthesis gas (syngas) using a partial oxidation (POX) reactor and a reforming exchanger.

BACKGROUND

Reforming of hydrocarbons is a standard process for the production of hydrogen-containing synthesis gas used for ammonia or methanol, for example. Conventional POX reactors are unpacked, free-flow, non-catalytic gas generators to which preheated hydrocarbon gas and oxygen are supplied, optionally with a temperature moderator. The partial oxidation reactor effluent is then quenched or cooled, typically to between 200 degrees C. and 300 degrees C., optionally cleaned to remove soot, and usually further converted in high and low temperature shift converters wherein CO and steam react to form additional hydrogen and CO2. Syngas with high hydrogen content is especially desirable for ammonia or other synthesis processes where hydrogen is the main reactant from the syngas. The steam to hydrocarbon weight ratio in the POX reactor feed is generally from 0.1 to 5, the atomic ratio of oxygen to carbon in the hydrocarbon is in the range from 0.6 to 1.6, and reaction times vary from 1 to 10 seconds.

POX reactors produce a syngas effluent at a very high temperature prior to quenching (for example, from about 1100 degree C. to about 1650 degree C.). This high temperature means that much of the hydrocarbon feed must, in effect, be used as a rather expensive fuel to preheat feeds and generate high- or medium-pressure steam. The steam production is usually far in excess of plant requirements and must therefore be exported, and frequently there is little or no market for the steam.

A need exists for a way to improve efficiency of hydrogen plants that use POX reactors and reduce or eliminate the steam export. It is also frequently desired to maximize or increase hydrogen production from an existing hydrogen plant; however, the POX reactor is frequently a capacity-limiting operation. POX reactors cannot easily be expanded to increase production.

The embodiments herein address at least these needs by supplying the partially cooled POX reactor process effluent to the shell side of a reforming exchanger to provide heat for additional syngas production. Reforming exchangers used with autothermal reformers are known, for example, from LeBlanc U.S. Pat. No. 5,011,625; LeBlanc U.S. Pat. No. 5,122,299; and Cizmer U.S. Pat. No. 5,362,454; all of which are hereby incorporated herein by reference in their entirety. These reforming exchangers are available commercially under the trade designation KRES or Kellogg Reforming Exchanger System.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description will be better understood in conjunction with the accompanying drawings as follows:

FIG. 1 is a simplified schematic process flow diagram of a conventional prior art POX process that can be retrofitted according to one or more embodiments herein.

FIG. 2 is a simplified schematic process flow diagram of a syngas process with a POX reactor and a reforming exchanger integrated according to one or more embodiments herein.

The embodiments are detailed below with reference to the listed Figures.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Before explaining the embodiments in detail, it is to be understood that the embodiments are not limited to the particular embodiments and that they can be practiced or carried out in various ways.

The present embodiments use a reforming exchanger in parallel with a partial oxidation (POX) reactor in a new hydrogen plant with improved efficiency and reduced steam export, or in an existing hydrogen plant. In one embodiment, the hydrogen capacity can be increased by as much as 20 to 30 percent with reduced export of steam from the hydrogen plant. The resulting process has very low energy consumption.

The present embodiments provide a process for preparing syngas. The method includes: partially oxidizing a first hydrocarbon portion with oxygen in a partial oxidation reactor to produce a first reactor effluent; cooling the first reactor effluent to a temperature from about 650 degrees C. to about 1000 degrees C.; supplying the first reactor effluent to a reforming exchanger; passing a second hydrocarbon portion with steam through a catalyst zone in the reforming exchanger to form a second reactor effluent; discharging the second reactor effluent from the catalyst zone to form an admixture with the first reactor effluent; passing the admixture across the catalyst zone in indirect heat exchange therewith to cool the admixture and heat the catalyst zone; and collecting the cooled admixture from the reforming exchanger.

The cooling can include introducing water into the first reactor effluent as a quench fluid, indirect heat exchange, or a combination of water quenching and indirect heat exchange. The indirect heat exchange can be used to preheat the second hydrocarbon portion in a cross exchanger. The catalyst zone can include catalyst tubes. The method can include supplying the second hydrocarbon portion to a tube side of the reforming exchanger and passing it through the catalyst tubes, and supplying the cooled first reactor effluent to a shell side inlet of the reforming exchanger. The shell side inlet can be adjacent an outlet end of the catalyst tubes. The method can further include supplying the first and second hydrocarbon portions in a weight ratio of from about 40:60 to about 95:5. More desirable, the first and second hydrocarbon portions can be supplied in a weight ratio of from about 40:60 to about 60:40 (for example, if for more efficient hydrogen production) or from about 80:20 to about 95:5 (for example, if more CO is desired).

The present methods for retrofitting a syngas process entail a partial oxidation reaction step for converting a first hydrocarbon stream to a first reactor effluent, a heat recovery step for cooling the first reactor effluent and producing steam with the recovered heat, and a downstream processing step for receiving the cooled reactor effluent and producing a product syngas of enhanced hydrogen content.

The retrofit can include partially cooling the first reactor effluent to a temperature from about 650 degrees C. to about 1000 degrees C. The partially cooled first reactor effluent is diverted to a reforming exchanger. A second hydrocarbon portion with steam is passed through a catalyst zone in the reforming exchanger to form a second reactor effluent. The refit can further include discharging the second reactor effluent from the catalyst zone to form an admixture with the first reactor effluent, passing the admixture across the catalyst zone in indirect heat exchange therewith to cool the admixture and heat the catalyst zone. The admixture from the reforming exchanger can be supplied to the heat recovery step.

With reference to the figures, FIG. 1 is a simplified schematic process flow diagram of a conventional prior art POX process that can be retrofitted according to one or more embodiments herein. Desulfurized natural gas or other hydrocarbon supplied from line 2 is mixed with process steam from line 4 and the mixture is preheated in a feed preheat exchanger (not shown). The preheated steam-hydrocarbon mixture can be fed via line 6 to a POX reactor 8 (or a plurality of POX reactors) with oxygen 10 and the effluent is collected in line 12, quenched with water injected via line 14, and then supplied to downstream processing 15 that can include a shift section (high temperature, medium temperature and/or low temperature shift converters), heat recovery, CO2 removal (pressure swing absorption or PSA, for example), and the like. A hydrogen-rich syngas stream 17 is produced.

The plant exampled in FIG. 1 is retrofitted, or a new plant is built, in accordance with one embodiment of one or more of the embodiments herein. FIG. 2 is a simplified schematic process flow diagram of a syngas process with a POX reactor and a reforming exchanger integrated according to one or more embodiments herein. The process effluent in line 12 from the POX reactor(s) 8 is quenched with process water via line 14 to a temperature from about 700 degrees C. to about 1100 degrees C. The mixture is supplied via line 16 to the shell-side inlet of the reforming exchanger 18. A heat exchanger 15 can be used in addition to, or in lieu of, quench line 14. The heat exchanger 15 can be used to preheat feed stream 19.

A preheated mixture in line 19 of steam and hydrocarbon, which can be the same or different as the hydrocarbon in line 2, is supplied to a tube-side inlet of the reforming exchanger 18. The mixture passes through the catalyst tubes 20 to form additional hydrogen-containing gas. The reformed gas from outlet openings of the catalyst tubes 20 mixes with the POX reformer effluent and the mixture passes across the outside of the catalyst tubes 20 to the shell-side outlet where it is collected in line 22 in a conventional manner. The combined syngas in line 22 is then supplied to conventional downstream processing 24 as exampled in FIG. 2, which can include a shift converter, a heat exchange unit for the recovery of heat, and further purification, producing purified molecular hydrogen. In the retrofit application, the downstream processing units can be modified or expanded as necessary to handle the additional syngas supplied via line 22 that results from the addition of the reforming exchanger 18.

The heat requirement for the reforming exchanger 18 is met by the quantity and temperature of the POX reactor effluent. Generally, the more feed in line 19 to the reforming exchanger 18, the more heat required from the POX reactor effluent 16 to sustain the generally endothermic reforming reaction in the catalyst tubes 20. The temperature of the reformer catalyst tube effluent gas is desirably as hot as the materials of construction of the reforming exchanger 18 will allow (for example, from about 750 degrees C. to about 1000 degrees C. in a KRES unit). If the temperature is too low, insufficient reforming can occur in the reforming exchanger 18, whereas if the temperature is too high the metallurgical considerations might become problematic.

The proportion of hydrocarbon feed to the POX reactor(s) 8 can range from 40 to 95 percent of the total, whereas the proportion to the reforming exchanger 18 can be from 5 to 60 percent of the total hydrocarbon feed. The feed split between the POX reactor(s) 8 and the reforming exchanger 18 is desirably such that the POX reactor(s) 8 must produce a suitable volume of hot effluent to provide the heat requirements of the reforming exchanger 18. A feed split to the POX reactor(s) 8 of from 0 to 60 percent of the total is beneficial for improved energy efficiency and maximizing the hydrogen production rate, whereas feeding from 80 to 95 percent of the total hydrocarbon feed to the POX reactor(s) 8 is beneficial for making more CO in the syngas.

The present embodiments can be illustrated by way of an example. Preliminary process design parameters for an integrated POX-reforming exchanger unit installed as exampled in FIG. 2 were developed based on the retrofit of the typical POX process exampled in FIG. 1 with the stream composition and flow rate for line 16 indicated in Table 1 below. Compositions, properties and flow rates for selected streams in the process modified in accordance with the configuration of FIG. 2 are also shown in Table 1.

TABLE 1 POX Reactor-Reforming Exchanger Configuration Stream ID: POX Catalyst Catalyst Shell-Side Effluent Tube 20 Tube 20 Outlet Line Line 16 Inlet Exit 22 Component Stream Composition, dry mole percent H₂ 62.35 1.80 73.79 64.21 N₂ 0.66 1.80 0.47 0.63 CH₄ 0.66 94.40 3.04 1.05 Ar 0.11 0.00 0.00 0.09 CO 33.26 0.10 16.52 30.54 CO₂ 2.96 0.20 6.17 3.49 C₂H₆ 0.00 1.20 0.00 0.00 C₃H₈ 0.00 0.30 0.00 0.00 i-C₄ 0.00 0.10 0.00 0.00 i-C₅ 0.00 0.10 0.00 0.00 Total Flow, kmol/hr 636.2 32.1 123.5 759.7 H₂O, kmol/hr 153.2 85.8 50.3 203.5 Total Flow, kmol/hr 789.4 117.9 173.8 963.1 Total Flow, kg/hr 10,528 2,073 2,073 12,601 Pressure (bar (a)) 32.4 35.5 32.4 32.1 Temperature (° C.) 999.7 308.8 938.1 702.3

In the base case with a POX reactor only, the syngas produced from the reforming section of the plant will have the composition and flow rate of the POX reactor effluent in line 16. Using the reforming exchanger in parallel with the POX reactor according to this embodiment of the invention, the effluent in line 16 is mixed with the gas exiting the catalyst tubes 20 to obtain a syngas having the composition in line 22. This example shows that an integrated POX-reforming exchanger process can be used to recover waste heat in the reforming exchanger and increase hydrogen production by 20 to 25 percent. Using process heat for the additional hydrogen generation in this manner yields a corresponding reduction in steam export.

While these embodiments have been described with emphasis on the embodiments, it should be understood that within the scope of the appended claims, the embodiments might be practiced other than as specifically described herein. 

1) A method for retrofitting a syngas process comprising a partial oxidation reaction step for converting a first hydrocarbon stream to a first reactor effluent through partial oxidation; a heat recovery step for cooling the first reactor effluent and producing steam with recovered heat; and a downstream processing step for receiving the cooled reactor effluent and producing a product syngas of enhanced hydrogen content, wherein the downstream processing step comprises: cooling the first reactor effluent to a temperature from about 650 degrees C. to about 1000 degrees C.; diverting the first reactor effluent to a reforming exchanger; passing a second hydrocarbon portion with steam through a catalyst zone in the reforming exchanger to form a second reactor effluent; discharging the second reactor effluent from the catalyst zone to form an admixture with the first reactor effluent; passing the admixture across the catalyst zone in indirect heat exchange therewith to cool the admixture and heat the catalyst zone; supplying the cooled admixture from the reforming exchanger to the heat recovery step. 2) The method of claim 1, further comprising introducing water into the first reactor effluent as a quench fluid. 3) The method of claim 1, further comprising cooling the first reactor effluent by indirect heat exchange. 4) The method of claim 1, further comprising heating the second hydrocarbon portion by indirect heat exchange before supplying the second hydrocarbon portion to the reforming exchanger. 5) The method of claim 1, further comprising introducing the second hydrocarbon portion to a tube side inlet of the reforming exchanger. 6) The method of claim 1, further comprising supplying the first reactor effluent to a shell side inlet of the reforming exchanger. 7) The method of claim 6, wherein the shell side inlet is adjacent an outlet end of the catalyst tubes. 8) The method of claim 1, wherein the catalyst zone comprises catalyst tubes. 9) The method of claim 1, wherein the indirect heat exchange comprises heating the second hydrocarbon portion in a cross exchange. 10) The method of claim 1 further comprising supplying the first and second hydrocarbon portions in a weight ratio of ranging from about 40:60 to about 95:5. 11) The method of claim 1, further comprising supplying the first and second hydrocarbon portions in a weight ratio of ranging from about 40:60 to about 60:40. 12) The method of claim 1, further comprising supplying the first and second hydrocarbon portions in a weight ratio of ranging from about 95:5 to about 80:20. 13) A method for retrofitting a syngas process comprising cooling the first reactor effluent to a temperature from about 650 degrees C. to about 1000 degrees C.; diverting the first reactor effluent to a reforming exchanger; passing a second hydrocarbon portion with steam through a catalyst zone in the reforming exchanger to form a second reactor effluent; discharging the second reactor effluent from the catalyst zone to form an admixture with the first reactor effluent; passing the admixture across the catalyst zone in indirect heat exchange therewith to cool the admixture and heat the catalyst zone; and supplying the cooled admixture from the reforming exchanger for cooling the first reactor effluent and producing steam with recovered heat. 